1. Field of the Invention
Present invention relates to a manufacturing method of a tire mold for molding a tire with vulcanization and specifically related to the laminated mold provided with a laminate consisting of a plurality of thin sheets laminated on each other in a widthwise direction and a manufacturing method thereof.
2. Description of the Prior Art
As shown by FIG. 8(a) and FIG. 8(b), so far has been used a vulcanization metal mold (50) comprising a plurality of sector molds (53) annularly coupled each of which is formed of a holder (52) by which a crown portion metal mold (51) having a cross sectional shape of the tire crown portion is held and the surface of a raw tire being already molded is press fit to an inner wall of the heated vulcanization mold (50) by pressurizing inner side of the molded tire and such application of heat and pressure to raw rubber has been employed as a method of vulcanization of tire. Usually, the above crown portion metal mold (51) can be manufactured by casting and yet, because such a casting mold not only costs much labor but also material cost is high, recently for meeting purpose of attaining low cost and reduction in delivery date in place of the above crown portion metal mold (51), which is a casting mold, a laminated mold as shown by FIG. 9(a) and FIG. 9(b) has become in use wherein the laminated mold comprises an annular tread pattern molding portion being formed by arranging a plurality of sector molds (63) in a peripheral direction of the tire wherein the crown portion metal mold (61) which consists of the laminate being formed of a plurality of thin sheets laminated, held by the holder (62) constitutes the sector mold (63). In this description (61s) denotes a lamination surface of the thin sheet (61), (61p) denotes an end face of the thin sheet on the side of the holder (62) and (61q) denotes an end face of the thin sheet on the side of contacting with the face of the tire stepping on the road surface (hereinafter, the wording “the face of the tire stepping on the road surface” is shortened to read “the tire stepping face”).
In view of automating and speeding up the manufacturing, the thin sheet (61a) is generally formed by means of a laser machining with 2DCAM. Thus formed thin sheets (61a) are laminated to form the laminate to be used as the crown portion metal mold (61) and by placing the crown portion metal mold (61) in the holder (62), the sector mold (63) having the laminate as the crown portion metal mold can be formed. Concretely speaking, as shown by FIG. 10 the thin sheet materials (61z) are cut at respective both ends by casting a laser beam perpendicularly to those thin sheet materials (61z) to become rectangularly shaped cross section and those thin sheet (61a) having thus formed rectangularly shaped cross section are laminated in a widthwise direction of the tire to form the tread pattern molding portion.
However, as long as relying on the above method, as shown by FIG. 9(a) due to the fact that the cross section of the thin sheet (61a) is rectangularly shaped, the crown portion metal mold (61), which is formed by coupling end faces (61q) of respective thin sheets (61a), inevitably becomes to have a profile stepped by the amount corresponding to the thickness of the thin sheets (61a) having the rectangularly shaped cross section. Accordingly, there have arisen problems such that not only appearance of the vulcanized tire is inferior but also its performance is inferior than that of the vulcanized tire manufactured through the casting mold currently in use. Furthermore, possibility of degradation in durability is anticipated because many protrusions with acute angle appear on the tire stepping face.
Further, in the case where the thin sheets are laminated in a peripheral direction of the tire, though close contact between those thin sheets can be assured on the inner side of radial direction, but on the outer side thereof gaps are inevitably produced therebetween and not only opening and closing operation of the mold becomes unstable but also degradation in its durability will be caused.
The present invention is made to cope with those problems so far have arisen and thus object of the present invention to provide a method for manufacturing the laminated mold capable of suppressing formation of stepped shape appearing on its profile comparing with the one as originally intended.